1. Field of the Invention
This relates to signal oscillators and, more particularly, to signal oscillators employing feedback regulation of frequency.
2. Description of the Prior Art
High accuracy conventional oscillators are characterized by their use of quartz crystals as the frequency determining elements. The use of crystals, however, precludes these oscillators from being fully integrable, i.e., capable of being realized in integrated circuit form. On the other hand, oscillators that are integrable generally employ resistors and capacitors as their frequency determining elements, but the time constants developed by these and other components in the circuit are temperature dependent thereby affecting the operating frequency and its precision with changing temperature.
In the art of feedback regulation of frequency, a technique employing both crystal and noncrystal (variable) oscillators is often used. The crystal oscillator is employed as a "standard" and a multiple of the variable oscillator is compared to the "standard" in a phase comparator. In turn, the error signal developed by the phase comparator is utilized to control the frequency of the variable oscillator. From the integrability standpoint, this arrangement, which generally is called a phase-lock loop, suffers from the same drawbacks that crystal oscillators do; to wit, the crystal oscillator cannot be fully integrated.